The single-page, computer-printed message was discovered Saturday after cops were called to the blood-spattered Flatbush basement apartment where Vindalee Smith, 38, had been stabbed and slashed across the throat.

“The note was underneath the body. They found it when they rolled her over,” one law-enforcement source said.

Typed in big, black block letters, the note warned that one pregnant woman a week would die unless Washington, DC, sniper Lee Boyd Malvo were sprung from prison, said a source familiar with the message.

But skeptical investigators believe the note is a ruse by the killer to throw them off track — although they are not ruling anything out, sources said.

Police believe Smith — who was a day away from getting married and two weeks from giving birth — knew her killer. There was no sign of forced entry, and no weapon was found.

Malvo, 27, is serving life in prison for six of the 10 Beltway sniper attacks that terrorized the country in 2002. He and his murderous mentor, John Allen Muhammad, had planned to kill six white people a day for a month.

Muhammad was executed in November 2009. Malvo was back in the news last month, when he acknowledged in a jailhouse interview that he was “a monster.”

There is no indication of any connection among Smith, her murderer and Malvo, law-enforcement sources said.

What the hell? Something really ain’t clean in the water. The note was a throw off letter to give a false lead to detectives. There are no “Master Minds” involved here.